1. Field of the Invention
This invention relates to a method of separating phenylalanine and cinnamic acid, and more specifically, it relates to a method of separating phenylalanine and cinnamic acid by contacting a mixed solution containing phenylalanine and cinnamic acid with a synthetic adsorbent under specific conditions.
2. Description of the Prior Art
Phenylalanine is one of essential amino acids and is used in pharmaceuticals, in particular, in medicinal amino acid transfusions etc., and recently it has aroused people's interest as an amino acid constituting .alpha.-aspartylphenylalanine methyl ester which is a peptide type sweetener.
Phenylalanine has heretofore been produced by a chemical synthetic process, a protein hydrolytic process, a fermentation process etc., but the production efficiency was low with any such process and efficient production processes have been studied.
As one of these processes, there is a process for producing L-phenylalanine from cinnamic acid as a starting material by an enzymatic reaction using L-phenylalanine ammonialyase in the presence of ammonia, and this process has been attracting attention as an industrial production process because the productivity of phenylalanine is extremely high.
However, in the above-described process, the produced L-phenylalanine is co-present with cinnamic acid and ammonia, and therefore, in order to obtain the L-phenylalanine as a single substance, it is necessary to separate and recover the L-phenylalanine from the mixture of those. But, since the phenylalanine and the cinnamic acid are similar in structure, it is difficult to separate them from each other. Therefore, in order to industrially advantageously produce L-phenylalanine, it is important to efficiently conduct the separation from the co-present cinnamic acid.
Under such circumstances, the present inventors have been intensively studying in pursuit of a method of efficiently separating and purifying phenylalanine co-present with cinnamic acid, and have discovered that by conducting treatment using a porous synthetic adsorbent under specific conditions, the separation of phenylalanine and cinnamic acid can be extremely efficiently achieved.
The porous synthetic adsorbent is composed of a crosslinked polymer obtained by polymerizing, polycondensing or co-polymerizing various organic polymeric monomers, or a crosslinked polymer obtained by polymerizing or polycondensing various polymeric monomers and thereafter crosslinking, and has significant levels of surface area and pore volume, and is utilized in the separation and purification of various substances, in particular, medicines, foods etc. Examples of the synthetic adsorbent are abundant, and, for example, they have been produced and found in market under such tradenames as "Diaion" HP 10, 20, 21, 30, 40, 50, "Diaion" HP 2 MG (produced by Mitsubishi Chemical Industries, Ltd.; trademark), "Amberlite" XAD 2, 4, 7, 8 (produced by Rohm & Haas Co., U.S.A.; trademark) etc.
It is already known that such synthetic adsorbents satisfactorily adsorb amino acids and organic acids; for example, it is also known that the amino acids are most favorably adsorbed in the vicinity of the isoelectric point, while the organic acids are well adsorbed under low pH conditions, i.e., where the organic acid is not dissociated.
Based on such a knowledge, the present inventors have been intensively studying on a method of separating and purifying phenylalanine from a mixed solution containing phenylalanine and cinnamic acid using a synthetic adsorbent, and, as a result, have come to discover that the adsorptions of phenylalanine and cinnamic acid by a synthetic adsorbent depend on the concentration of a co-present salt, and, surprisingly, the relative adsorption (selectivity in adsorption) of phenylalanine relative to cinnamic acid greatly varies depending on the concentration of the co-present salt, and therefore that by wisely utilizing these phenomenons, the separation of phenylalanine and cinnamic acid may be extremely efficiently effected, thereby having accomplished this invention.